1. Field of the Invention
The present invention relates to an apparatus for measuring dynamic load characteristics of wheels (tires) of an automobile. More particularly, the invention relates to an apparatus for measuring load (dynamic load) exerted on the wheels of an automobile that is traveling.
2. Description of the Related Art
It was so far difficult to measure the load, i.e., dynamic load exerted on the four wheels of an automobile that is traveling and, hence, it has not been able to easily and fully grasp the degrees of load exerted on the tires. So far, it was generally accepted practice to measure the degree of wear of the tires after running or to measure the surface temperature of the tire treads, to infer the dynamic load exerted on the tires.
Further, it was difficult to quantitatively grasp a change in a rolling caused by a shifting amount of load between the right and left wheels, cornering performance of the test tires for the respective dynamic loads, and the marginal coefficient of friction between the tire and the road surface.
In developing tires for use in a race, it is important to quantitatively grasp the dynamic load characteristics of the test car and it inevitably becomes an indispensable requirement to measure the dynamic loads exerted on the four wheels, since such tires must satisfy turning performance, braking performance and performance on a wet road of an automobile that is constructed in an ever sophisticated manner in recent years.
According to Japanese Unexamined Patent Publication (Kokai) No. 6-227225, a quartz piezoelectric element that generates electric charge when a force is exerted thereon is incorporated in a suspension system or in a support system of a vehicle, ruggedness of the road or track is detected relying upon the magnitude and direction of the load measured by the quartz piezoelectric element, a hydraulic or pneumatic mechanism is controlled by a servo mechanism based on the detected data, in order to suppress the rolling of the vehicle caused by the ruggedness of road or track.
However, it is expensive to use such a quartz piezoelectric element disclosed in Japanese Unexamined Patent Publication (Kokai) No. 6-227225, and it is difficult to attach the quartz piezoelectric element to a suitable portion of the vehicle. Depending upon the place where the quartz piezoelectric element is installed, further, it becomes difficult to fully correctly grasp the dynamic load characteristics of the wheels during the vehicle is traveling.
In view of the above-mentioned circumstances, it is an object of the present invention to provide an apparatus for measuring dynamic load characteristics of wheels, which can be relatively easily installed on a portion between the body of the vehicle and the wheel to receive force from the road surface, which is cheap yet makes it possible to grasp the dynamic load characteristics of the wheel during the travel of the vehicle, maintaining a sufficient degree of accuracy.
In order to accomplish the above-mentioned object according to the present invention, there is provided an apparatus for measuring dynamic load characteristics of wheels, comprising a washer-type strain sensor incorporated between a body of a vehicle and a wheel at a portion where it receives force from a road surface, and a means for measuring an output of the washer-type strain sensor while the vehicle is traveling. The washer-type strain sensor is distorted depending on the dynamic load which the wheel receives from the road surface and generates a voltage corresponding to the strain.
In the present invention, the washer-type strain sensor is incorporated in a portion where a shock absorber of a suspension system is attached to the main body of the vehicle. In this case, the washer-type strain sensor is attached between the main body of the shock absorber of the suspension system of the vehicle and a spring, the lower end of which is in contact with the lower seat on the side of the wheel. Further, the washer-type strain sensor is held between the main body of the shock absorber and between it and the spring by means of a first attachment and a second attachment that are interposed between them, respectively. Therefore, the washer-type strain sensor is allowed to directly receive the load from the road surface, i.e., to directly receive the load that is received by the spring.
A recessed portion is formed in a surface of the first attachment that comes in contact with the washer-type strain sensor except for an outer circumferential portion thereof that comes in contact with the washer-type strain sensor. Being corresponded thereto, a recessed portion is formed in the surface of the washer-type strain sensor that comes in contact with the first attachment except for an outer circumferential portion thereof that comes in contact with the first attachment. Therefore, even when the washer-type strain sensor is distorted by the dynamic load of the wheel, interference of the washer-type strain sensor with the first attachment is avoided.
A surface of the washer-type strain sensor that comes in contact with the second attachment is protruded except for an outer circumferential portion thereof, and the protruded surface comes in contact with the second attachment. Accordingly, the washer-type strain sensor directly receives the load from the spring through the protruded surface.
According to the present invention, there is further provided an apparatus for measuring the dynamic load characteristics of wheels, comprising:
a washer-type strain sensor incorporated between a body of a vehicle and a wheel, at a portion where it receives force from the road surface to detect the dynamic load of the wheel;
a sensor for detecting a vehicle speed;
a sensor for detecting a steering angle;
a sensor for detecting a gravitational acceleration (G) in the lateral direction and a gravitational acceleration (G) in the longitudinal direction;
a sensor for detecting a yawing angle of the wheel;
a sensor for detecting a damper stroke; and
a means that receives signals from these sensors to measure a change in a rolling caused by the shifting amount of dynamic load of the wheel, cornering performance of a test tire for respective dynamic loads, and a marginal coefficient of friction between the tire and a road surface.
According to the present invention as described above, it is made possible to correctly measure the loads on the four wheels while the vehicle is traveling, to grasp the load on the tires, cornering performance of the tires for the respective dynamic loads and marginal coefficient of friction between the tire and the road surface in terms of numerical values, and, hence, to quantitatively evaluate the specifications of the tires concerning sophisticated turning performance, braking performance and performance on a wet road.